Arylamine compounds can be used as hole transport materials for photoreceptor applications. In electrophotography, an electrophotographic imaging member may include the following active layers: (1) a charge generating layer containing a light-absorbing material, and (2) a charge transport layer containing charge transport molecules or materials. A hole transport material is a material that facilitates the transport of charge over the surface of the electrophotographic imaging member.
Many hole transport materials for photoreceptor applications contain hydroxy arylamine functionality. The term “arylamine” refers, for example, to moieties containing both aryl and amine groups. Exemplary aralkylene groups have the structure Ar—NR1R2, in which Ar represents an aryl group and R1 and R2 are groups that may be independently selected from hydrogen and substituted and unsubstituted alkyl, alkenyl, aryl, and other suitable functional groups. Production of a number of arylamine compounds, such as arylamine compounds that are useful as charge-transport compounds in electrophotographic imaging devices and processes, often involves synthesis of intermediate materials, some of which generally are costly and/or time-consuming to produce, and some of which involve a multi-step process.
For example, such hydroxy arylamine compounds are typically prepared via deprotection of an alkyl arylamine ether using trimethyl silyliodide or trimethyl silylchloride and sodium iodide in sulfolane. For example, a typical preparation of a hydroxy arylamine compound, N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-[1,1′-biphenyl]-4,4′-diamine, from a methoxy arylamine compound, N,N′-diphenyl-N,N′-bis(3-methoxyphenyl)-[1,1′-biphenyl]-4,4′-diamine, is described below:

N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-[1,1′-biphenyl]-4,4′-diamine is obtained by the demethylation of N,N′-diphenyl-N,N′-bis(3-methoxyphenyl)-[1,1′-biphenyl]-4,4′-diamine with trimethyl silylchloride and sodium iodide, in the presence of water, with sulfolane as the reaction solvent. The reaction is carried out at 60-65° C. for 6-7 hours under a nitrogen atmosphere. Aqueous sodium hydroxide scrubbers are used to neutralize methyl iodide, hydrogen iodide, and hydrochloric acid released during the reaction. Acidic volatile by-products are vacuum distilled prior to the precipitation of the crude N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-[1,1′-biphenyl]-4,4′-diamine-sulfolane adduct by the addition of deionized water. The crude adduct is washed with aqueous sodium thiosulphate solutions and deionized water for iodide removal. The crude material undergoes three purification steps. The crude is dissolved in acetone by heating to 55° C. and reprecipitated by the addition of deionized water, for the removal of sulfolane and the formation of a N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-[1,1′-biphenyl]-4,4′-diamine-water adduct. The N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-[1,1′-biphenyl]-4,4′-diamine-water adduct is heated to 55° C. in acetone for dissolution and reprecipitated by the addition of heptane, for the removal of water and the formation of a N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-[1,1′-biphenyl]-4,4′-diamine-acetone adduct. The N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-[1,1′-biphenyl]-4,4′-diamine-acetone adduct is refluxed in heptane for azeotropic removal of acetone to give the purified N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-[1,1′-biphenyl]-4,4′-diamine monomer.
This reaction is lengthy, can lead to higher costs, and can be very difficult to perform. The procedure requires a scrubber on the reaction to trap any methyl iodide, hydrogen iodide, and hydrochloric acid that is released during the reaction. The purification is complicated since the acidic volatile by-products must be removed by vacuum distillation prior to the precipitation or else side reactions can occur during the workup. An efficient process for the deprotection of arylamine compounds containing aromatic methyl ether groups is lacking in the industry.
Magano et al., 2-(Diethylamino)ethanethiol, a New Reagent for the Odorless Deprotection of Aromatic Methyl Ethers, J. Org. Chem., vol. 71, 2006, pages 7103-7105, describes a new reagent for the deprotection of electron-deficient aromatic methyl ethers using 2-(diethylamine)ethanethiol. This compound is commercially available as a hydrochloric acid salt, is odorless during the purification, and leads to an easy purification procedure because an extraction can be performed to remove both the deprotecting reagent and the byproduct, 2-(diethylamino)ethyl methyl sulfide into the aqueous phase by quenching with dilute acid. However, according to Magano et al., these conditions are only suited to compounds which contain electron withdrawing groups on the aromatic ring. See Magano et al. at page 7105 (“The major limitation for this methodology has to do with the absence of electron-withdrawing groups on the ring.”).
The reaction is performed by mixing the reagent, 2-(diethylamine)ethanethiol hydrochloric acid with sodium tert-butoxide in a solvent such as dimethylformamide, n-methyl-2-pyrrolidone, tetrahydrofuran, and dimethyl sulfoxide. The methoxy substituted substrate, is then added and the reaction heated at reflux until the reaction is complete. A workup and purification is then performed to give the desired hydroxy substituted compound.